| Criteria | Epithelial Cells | Endothelial Cells | Remarks |
| Definition | Cells forming the outermost layers of body surfaces and internal linings of cavities | Specialized epithelial-like cells that line the interior surface of blood and lymph vessels | Endothelial cells are a subtype of epithelial-like cells with unique vascular functions. |
| Origin | Derived from all three germ layers: ectoderm, mesoderm, and endoderm | Primarily derived from the mesoderm | Despite similar morphology, their embryonic origins differ, especially in developmental pathways. |
| Location | Found on skin, mucosal surfaces, respiratory and gastrointestinal tracts, glands | Lining blood vessels, heart chambers (endocardium), and lymphatic vessels | Epithelial cells cover external and internal surfaces; endothelial cells are exclusively within vascular structures. |
| Function | Protection, absorption, secretion, and sensory reception | Regulation of vascular tone, permeability, blood flow, leukocyte trafficking, and angiogenesis | Epithelial cells act as barriers and functional interfaces; endothelial cells control vascular physiology. |
| Polarity | Highly polarized with apical and basal surfaces | Also polarized but adapted for selective exchange between blood and tissues | Both exhibit polarity, but their surface specialization varies with function. |
| Cell Junctions | Tight junctions, adherens junctions, desmosomes, and gap junctions | Similar junctions but specialized for vascular permeability (e.g., tight and adherens junctions) | Both maintain barrier functions, but endothelial junctions are more dynamic to allow selective permeability. |
| Basement Membrane Association | Rest on a well-defined basement membrane | Also rest on a basement membrane | Both are anchored to basal lamina, contributing to structural integrity and signaling. |
| Cell Turnover and Renewal | Rapid turnover in tissues like skin and gut | Slower turnover, though capable of proliferation under stress or injury | Regenerative capacity varies depending on tissue type and physiological conditions. |
| Morphology | Varies from squamous, cuboidal, to columnar depending on location and function | Typically simple squamous to allow efficient exchange | Morphological differences reflect functional specialization—barrier vs exchange. |
| Markers | Cytokeratins, E-cadherin, EpCAM | CD31 (PECAM-1), von Willebrand factor, VE-cadherin, CD34 | Specific molecular markers help distinguish these cell types in immunostaining and flow cytometry. |
| Permeability Regulation | Generally low permeability, tight regulation | Highly regulated permeability depending on tissue (e.g., brain vs liver vasculature) | Endothelial cells dynamically regulate barrier function (e.g., blood-brain barrier vs fenestrated capillaries). |
| Involvement in Diseases | Cancer (e.g., carcinomas), inflammation, cystic fibrosis | Cardiovascular disease, thrombosis, atherosclerosis, angiogenesis in cancer | Both play roles in pathologies, often tissue-specific; endothelial dysfunction is key in vascular diseases. |
| Immune Interaction | Can express MHC molecules; involved in immune response at barriers | Actively participate in immune surveillance, leukocyte adhesion, and transmigration | Endothelial cells are essential gatekeepers for immune cell trafficking. |
| Role in Development | Involved in organogenesis and epithelial-mesenchymal transitions (EMT) | Critical for vasculogenesis and angiogenesis during embryonic development | Both are essential during embryogenesis but function in different developmental contexts. |
| Experimental Models | Used in organoid culture, wound healing, barrier assays | Used in vascular models, flow chamber assays, angiogenesis assays | Both are important for in vitro modeling of physiological and pathological processes. |
